The present invention relates to a method and a device for detecting at least one signal for a computer, the signal being converted by a converter device.
Many different converter devices are known from the related art, in particular analog-to-digital converters and digital-to-analog converters. Such converter devices or signal converters are used in the related art for converting physical quantities to a voltage, for example.
Corresponding converter modules are known from the technical book xe2x80x9cPC-gesteuerte Mexcex2technikxe2x80x9d (PC-Controlled Measurement Technology) by Klaus Dembowski from Marktund Technik-Verlag in 1993 (ISBN 3-87791-516-7), pages 169 through 206, where it is pointed out that in many cases, a converter module requires an additional periphery of analog and digital components to make it possible to work accordingly. For example, a multiplexer is required for detecting signals in multiple channels.
German Published Patent Application No. 37 00 987 describes a device for detecting an electric voltage signal for processing in a microcomputer in which at least one analog-to-digital converter is provided with a word of n bits, and in which it is possible to display the voltage to be measured by an additional digital-to-analog converter and an external circuit with the same accuracy of n bits, but with a higher monotonic resolution over the entire measurement range. The complete monotony of the more highly resolved measurement result is then achieved by software routines in the microcomputer on the basis of simple limit value comparisons.
The accuracy of such converter devices depends first on the signal level, in particular the voltage, for which the converter device or the computer containing it is intended, and secondly, it depends on the resolution of the converter device.
In general, it is known that signal matching can be performed with the help of a matching arrangement, e.g., a voltage divider.
Thus, if the level of the signal to be detected is different from the intended signal level at the input of the converter device, signal matching could be performed by a matching arrangement, but inaccuracies in the matching arrangement would be reflected directly in the conversion result. Thus, if the signal level of the signal to be measured or converted is different from, in particular higher than, the maximum signal level intended for the converter device, in particular the A/D converter, then it could be converted by a matching arrangement, in particular a voltage divider, only with a lower accuracy. Influencing quantities here include, for example, the temperature, inaccuracies in the matching arrangement, in particular in the resistors of a voltage divider, and aging phenomena, in particular in the resistors of the voltage divider. This loss of accuracy is manifested in a very interfering manner in particular since the inaccuracies in the converter device itself, e.g., due to nonlinearities or offset, usually turn out to be lower by a power of 10 than the inaccuracies in the matching arrangement, in particular the voltage divider.
An object of the present invention is thus to compensate for the loss of accuracy when using a matching arrangement which matches the input signals or the input signal level to the intended signals of the converter device or the computer containing the converter device and thus to compensate, i.e. to achieve an increase in accuracy. An improvement in the properties of a converter device, in particular an analog-to-digital converter, is thus to be achieved in this regard. In the concrete case of the analog-to-digital converter, this means that a 5V input signal, for example, can be applied via a voltage divider as a matching arrangement to a 3V analog-to-digital converter or to the corresponding input of a computer and converted without any loss of accuracy.
This object is achieved by a method and a device for detecting at least one first signal for a computer, the first signal being converted to a second signal by a converter device. In an advantageous manner, a first reference signal is applied to a reference device which converts it to a second reference signal, the second reference signal being switched to a converter device which converts it to a third reference signal, the second reference signal also being switched to a matching arrangement which matches the second reference signal to a fourth reference signal, the fourth reference signal also being switched to the converter device which converts it to a fifth reference signal, a correcting quantity being determined from a comparison of the third reference signal and the fifth reference signal in the computer, and the first signal being detected as a function of this correcting quantity.
In an expedient embodiment, the first signal is detected as a function of the correcting quantity in such a way that the first signal is converted to the second signal as a function of the correcting quantity, and the first signal is detected by analyzing the second signal, so that the correcting quantity determined has an influence on the conversion itself.
A next expedient embodiment is characterized in that the first signal is detected as a function of the correcting quantity in such a way that the first signal is converted to the second signal, and the second signal is matched to a third signal as a function of the correcting quantity, the first signal then being detected by analyzing the third signal, so the second signal converted from the first signal is linked to or influenced by the correcting quantity.
In this way, a computer having a first voltage, e.g., 3V, can convert signals having a different voltage, in particular a higher voltage, e.g., 5V, by using a normal matching arrangement, such as an internal or external voltage divider with a greatly improved accuracy, in particular in the case of an input signal having a voltage higher than the voltage at which the computer operates.
This makes it possible to eliminate process costs in the computer for a special converter device, usually an additional device, in particular an analog-to-digital converter, having a voltage different from the computer voltage. On the other hand, only low additional costs are incurred by integrating or attaching the device according to the present invention or the elements and connections thereof which are not yet included.
The correcting quantity can be determined repeatedly to advantage at preselectable intervals, which may be the same or different, and/or as a function of times of certain events, e.g., clocked signal acquisition. This method can thus also be used repeatedly in the operation of the computer in an advantageous manner to compensate for temperature-dependent changes or leakage currents, for example. This also makes it possible to eliminate changes in the matching arrangement due to aging, so a loss of accuracy in this regard can at least be compensated, and in general a definite increase in accuracy can even be achieved, because even internal inaccuracies, including those not due exclusively to the matching arrangement, can be compensated according to the present invention.
In addition, it is also advantageous that the first reference signal can be preselected to be variable so that the third reference signal, which is converted by the converter device, and the first reference signal correspond within preselectable tolerances, in particular they are identical at a desired tolerance of 0. In the case of a digital-to-analog converter as a reference device, this means in concrete terms that the voltage can be applied with a very high accuracy, because voltage is read back over the same circuit or an identically dimensioned circuit, and thus the voltage, which has undergone a digital-to-analog conversion, can be corrected. This control mechanism makes it possible to use matching arrangements which have a lower accuracy and are therefore less expensive.